1. Field of the Invention
The present invention relates to a method of fabricating an organic thin film transistor and a method of surface treatment for a gate insulating layer of an organic thin film transistor.
2. Description of Related Art
Organic thin film transistors (OTFTs) are currently the focus of considerable research due to their low fabricating cost, rollability, and large display area. OTFTs can be divided into top contact OTFTs and bottom OTFTs according to their structure. A top contact OTFT is generally composed of a substrate 10; a gate electrode 11 formed on the substrate 10; a gate insulating layer 12 formed on the gate electrode 11, an organic semiconductor layer 13 formed on and covering the whole gate insulating layer 12, and a source electrode 14 and a drain electrode 15 formed on the organic semiconductor layer 13, as shown in FIG. 1.
Referring to FIG. 2, in which a bottom contact OTFT is shown, a conventional bottom contact OTFT is generally composed of a substrate 10; a gate electrode 11 formed on the substrate 10; a gate insulating layer 12 formed on the gate electrode 11; a source electrode 14 and a drain electrode 15 formed on the gate insulating layer 12; and an organic semiconductor layer 13 formed on and covering the source electrode 14, the drain electrode 15, and the gate insulating layer 12.
In the fabrication of an OTFT, if an organic semiconductor layer is formed on a gate insulating layer with high hydrophobicity (i.e. low surface energy), a better electric characteristic of the organic semiconductor layer can be obtained. In a conventional method, a surface treatment is applied to improve the hydrophobicity of the surface of the gate insulating layer, which forms a self-assembled monolayer (SAM) on the gate insulating layer to transform the hydrophlic surface property into hydrophobic surface property of the gate insulating layer, in which octadecyltrimethoxysilane (ODMS), octadecyltrichlorosilane (OTS), etc. may be used as the material of the self-assembled monolayer. In another surface treatment method, plasma is utilized to increase the hydrophobicity of the surface of the gate insulating layer and improve the electric characteristic of the organic semiconductor layer.
However, the self-assembled monolayer (SAM) is usually made of materials with low dielectric constant, therefore when the SAM is applied to the surface treatment of the gate insulating layer, the capacity of the gate insulating layer may decrease, the operating voltage of the device may be raised, and the workload of the low-energy-consumption devices may also be increased. Alternatively, if plasma is used for the surface hydrophobic treatment of the gate insulating layer, the bombarding of the plasma may cause damage of the surface of the gate insulating layer and destroy the dielectric characteristic of the gate insulating layer. In a plasma surface treatment process, the material of the substrate should be specially limited (for example, a plastic flexible substrate may not be used) due to the applied high temperature (about 300° C. or above). Hence, the plasma-based surface treatment process is not suitable to be applied to flexible OTFT surface treatment. Besides, economical efficiency may decrease because expensive plasma equipment for OTFT surface treatment is required.
Therefore, it is desirable to provide an improved surface treatment method (or a method for increasing the hydrophobicity) for the surface of the gate insulating layer, which can be applied under low temperature conditions and also has advantages of low manufacturing cost and simple processing steps, and enables high hydrophobicity and lowers the surface energy of the gate insulating layer, and can improve the electric characteristic of the organic semiconductor layer without destroying the surface and decreasing the capacity of the gate insulating layer.